1. Field of the Invention
The present invention relates to the field of semiconductor wafer processing and, more particularly, to a two-piece chuck for supporting a wafer in a processing chamber.
2. Related Application
This application is related to a co-pending application titled xe2x80x9cCompliant Wafer Chuck;xe2x80x9d Ser. No. 09/293,012; filed Apr. 16, 1999; issued as U.S. Pat. No. 6,241,925.
3. Background of the Related Art
Various processing chambers are known in the art for processing semiconductor wafers, such as silicon wafers. Present practices include the manufacture of integrated circuit devices on the wafer by fabricating multiple levels of conductive (typically metal) layers above a substrate of the wafer. The multiple metallization layers are employed in order to accommodate higher densities as device dimensions shrink. Likewise, the size of interconnect structures also need to shrink in order to accommodate the smaller dimensions. The various processing chambers are utilized to deposit or remove materials in order to fabricate the integrated circuits. For example, deposition techniques include processes such as physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, and immersion of the wafer in an electrolyte. Similarly, a number of techniques are known for removing a material from a wafer. These techniques include reactive ion etching (RIE), plasma etching, chemical-mechanical polishing (CMP), and immersion of the wafer in an electrolyte.
Typically, the practice involves the complete placement of a wafer or wafers in the processing chamber. In single wafer processing, the wafer is typically placed on a chuck, which resides or is made to reside within the confines of the chamber. The chuck may be rotated to rotate the wafer. The chucks provide a hard upper surface upon which the wafer resides. The chuck is positioned so that all of the wafer resides within the interior walls of the processing chamber.
However, another line of processing chambers utilize the wafer to form the floor of the containment area for the processing fluid. For example, in a processing chamber described in U.S. Patent Application entitled xe2x80x9cProcess chamber and Method for Depositing and/or Removing Material on a Substrate;xe2x80x9d Ser. No. 08/916,564; filed Aug. 22, 1997; and assigned to the assignee of this application, a processing surface of the wafer forms the floor of the inner containment chamber, which holds the processing fluid for processing the exposed wafer surface. Another example of a processing chamber in which the wafer forms the floor of the containment vessel is described in U.S. Patent Application entitled xe2x80x9cMethod and Apparatus for the Disposal of Processing Fluid Used to Deposit and/or Remove Material on a Substrate;xe2x80x9d Ser. No. 09/118,362; filed Jul. 17, 1998; and also assigned to the assignee of this application.
In both examples, the processing fluid is an electrolyte for processing the wafer. The electrolyte is retained in the confined area bounded by the sidewalls and the wafer, which wafer forms the base or floor of the confined area. In order to achieve this confinement, the sidewalls (at least a portion of it) mate to the periphery (edge) of the wafer. Generally, once the wafer is placed upon a chuck, the chuck and the wafer are raised until the wafer edges mate to the bottom surface of the sidewalls of the containment vessel. A seal, such as an O-ring, is typically required to hold the fluid within the vessel and/or to protect electrodes, where electrodes are mated to the outer edge of the wafer.
When prior art chucks are utilized, two significant problems are noted. These problems are generally attributable to the solid one-piece design of the chucks. In order to maintain tight seal integrity around the circumference of the wafer""s edge where the sidewall joins the wafer surface, the mating boundary between the sidewall and the wafer""s surface cannot exceed a given tolerance. Yet, due to mis-alignment, tolerance imperfections, pressure changes within the vessel, O-ring wear and deterioration (as well as for other reasons), it is difficult to maintain tight seal integrity at the boundary. This is further complicated when a thin O-ring is used. A thin O-ring is desirable in order not to reduce the processing area on the face of the wafer. Maintaining a tight tolerance is difficult to achieve using thin O-rings. Also, with thinner O-rings the seal integrity breakdown can occur at much lower pressure.
The problem is amplified when larger diameter wafers are being processed, since the contact area is over a larger circumference. Since the wafer is residing on a flat rigid surface of the chuck, the wafer is not flexible to adjust to any gap separation distance which exceeds the tolerance. The leakage of the fluid can adversely affect the performance of the system, since the fluid can contact the backside of the wafer itself and/or the electrodes contacting the edge of the wafer (if such electrodes are present).
The second problem is leakage and/or wetting on the underside of the wafer. Typically, the electrolyte is prevented from leaking to the underside of the wafer when the wafer is engaged to the chamber. When the wafer is washed/rinsed to remove the electrolyte, the wafer is lowered, in order to be disengaged from the chamber. At this lower position, the cleaning of the wafer is performed, typically by the spraying of deionized water. During this cleaning procedure, there is a tendency for the water to penetrate between the underside of the wafer and the chuck surface. Even if a seal is present, the water penetration is likely, since the edge of the chuck resides proximal to the wafer""s edge. Furthermore, the presence of vacuum on the chuck surface to hold the wafer in place during the rinse and spin cycle can attract and/or retain liquid droplets. That is, the vacuum, not only attracts the liquid, but can also retain the liquid in the vacuum opening or channel. Subsequently, when the vacuum is removed, such as to remove the wafer, the liquid spurts from the vacuum opening and wets the underside of the wafer. When the wafer is removed, even after a spin dry cycle which removes the liquid from the face of the wafer, the liquid is present on the underside of the wafer.
Accordingly, what is needed is a scheme in which unwanted sidewall-wafer gap separation is reduced or prevented when semiconductor wafers are processed in a processing chamber, especially where the wafer forms the floor of the containment region. Furthermore, it would be beneficial for the chuck to reduce the risk of backside wetting.
A two-piece wafer chuck for supporting a substrate. The chuck is comprised of a base plate for supporting an outer peripheral area of the wafer residing thereon and a central disk, which resides within a central open region of the base plate. When mounted, the base plate moves relative to the fixed central disk so that the wafer edges can tilt to properly mate to a processing chamber. The base plate is coupled to an inner shaft which allows the base plate to be lowered relative to the central disk, in order to expose the underside of the wafer.